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Preface

The basic principle of master-slave replication of MySQL is to connect from the library to the master library, and the master library generates a master library DUMP thread. The main task of the DUMP thread is

The binlog log is mined all the time, and then sent to the IO thread of the slave library. After receiving the log stream, the IO thread writes to relay log, another line.

The program relay log thread reads the contents of the sql and then replays the SQL statement.

This article mainly introduces you about the state transition of MySQL master-slave replication thread. Let's take a look at the detailed introduction.

1. The thread status (State) value of the main library

The following list shows the most common state (SHOW PROCESSLIST) that you might see in the State column of the Binlog Dump thread of the master server in the master-slave replication. If the Binlog Dump thread is not visible on the primary server, this means that the replication is not running, that is, no Slave hosts are currently connected.

Sending binlog event to slave

The binary log consists of various events, and an event is usually an update plus some other information. The thread has read an event from the binary log and is sending it to the slave server.

Finished reading one binlog; switching to next binlog

The thread has finished reading the binary log file and is opening the next log file to be sent to the slave server.

Has sent all binlog to slave; waiting for binlog to be updated

The thread has read all major updates from the binary log and has sent them to the slave server. The thread is now idle, waiting for new events to appear in the binary log caused by new updates on the primary server.

Waiting to finalize termination

A very simple state that occurs when a thread stops.

Second, the thread state (State) value from the library Imax O

Connecting to master

The thread is trying to connect to the primary server.

Checking master version

A temporary state that occurs immediately after a connection with the primary server is established.

Registering slave on master

A temporary state that occurs immediately after a connection with the primary server is established.

Requesting binlog dump

A temporary state that occurs immediately after a connection with the primary server is established. The thread sends a request to the primary server for the contents of the binary log starting from the requested binary log file name and location.

Waiting to reconnect after a failed binlog dump request

If the binary log dump request fails (because there is no connection), the thread goes to sleep and then periodically attempts to reconnect. You can use the-master-connect-retry option to specify the interval between retries.

Reconnecting after a failed binlog dump request

The thread is trying to reconnect to the primary server.

Waiting for master to send event

The thread is connected to the primary server and is waiting for the binary log event to arrive. If the primary server is idle, it will last for a long time. If the wait lasts for slave_read_timeout seconds, a timeout occurs. At this point, the thread thinks the connection is broken and attempts to reconnect.

Queueing master event to the relay log

The thread has read an event and is copying it to the relay log for processing by the SQL thread.

Waiting to reconnect after a failed master event read

An error occurred while reading (because there is no connection), and the thread will sleep for master-connect-retry seconds before attempting to reconnect.

Reconnecting after a failed master event read

The thread is trying to reconnect to the primary server, and when the connection is reestablished, the state changes to Waiting for master to send event.

Waiting for the slave SQL thread to free enough relay log space

A non-zero relay _ log_space_ value is being used, and the relay log has grown to a combined size that exceeds that value. The Icano thread is waiting until the SQL thread processes the contents of the relay log and deletes some of the relay log files to free up enough space.

Waiting for slave mutex on exit

A very simple state that occurs when a thread stops.

3. SQL thread status (State) value from the library

Reading event from the relay log

The thread has read an event from the relay log and is ready to process the event.

Has read all relay log; waiting for the slave I/O thread to update it

The thread has processed all the events in the relay log file and is now waiting for the I / O thread to write the new event to the relay log.

Waiting for slave mutex on exit

A very simple state that occurs when a thread stops.

Fourth, connect thread status (State) values from the library

These thread states occur on the replication slave library, but are associated with the connection thread, not with the Imax O or SQL thread.

Changing master

The thread is processing the CHANGE MASTER TO statement.

Killing slave

The thread is processing the STOP SLAVE statement.

Opening master dump table

This state occurs after Creating table from master dump.

Reading master dump table data

This state occurs after Opening master dump table.

Rebuilding the index on master dump table

This state occurs after Reading master dump table data.

Summary

The above is the whole content of this article, I hope that the content of this article has a certain reference and learning value for your study or work, if you have any questions, you can leave a message and exchange, thank you for your support.

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